Friday 1 April 2011 19.05 EDT
First published on Friday 1 April 2011 19.05 EDT

In terms of probability, there's no reason why a coin tossed 100 times shouldn't come down heads each time; why all the air molecules in your living room shouldn't suddenly rush out of the window; or why a hurricane whirling through Alabama shouldn't reorganise a junkyard full of scrap metal into a full-scale replica of a 737 airliner. When the third of those logical outrages actually occurs, notice is taken by the DEI, a terrifically obscure government agency established for just such an eventuality. Spy cameras are deployed, intelligence feeds combed. An intercepted fragment of anonymous text seems to suggest a bizarre invention: a Coincidence Engine, built to interfere with probability. A reclusive mathematical genius called Nicolas Banacharski may be responsible. No one knows, because his hut has burned down and he's gone missing. Meanwhile Alex Smart, a postgrad supervised by a correspondent of Banacharski's, has suddenly and unexpectedly fled Cambridge for the US. Is it possible Alex has the Coincidence Engine? If the monstrous thing exists, can anything still be considered impossible?

The first novel from a former literary editor of the Daily Telegraph, The Coincidence Engine is, more or less, a comedy thriller. There's a black helicopter; a surreptitious rendezvous in a diner; a nocturnal shootout on a building site. The head of the DEI is known only as Red Queen, and one of its field agents sports three aliases before page 4. "DEI" stands, we are told, for the Directorate of the Extremely Improbable. "It's a silly name," Red Queen admits, "but it's always been called that, and the silliness acts as a sort of camouflage."

The silliness multiplies across Sam Leith's pages like fractal rainbows. There's farcical misprision in the plight of Alex, the innocent abroad, who's actually driving from Atlanta to San Francisco to propose to his girlfriend. Slapstick is provided by a pair of bumbling hitmen sent to tail him, while merry nonsense blossoms from a nexus of improbability that seems to accompany him across the continent. Wherever Alex passes, quite unknown to him, birds start whistling "Amazing Grace", long-lost siblings bump into each other at the dry cleaners', and the highway fills up with identical silver Pontiacs. There's plenty of intellectual comedy too. I particularly liked the theory that the Coincidence Engine can't be found because it keeps arranging for its hunters to win the lottery. They become so rich they give up their jobs.

The Coincidence Engine is an absurdist novel of ideas, comparable to the books of Robert Anton Wilson: anarchic, psychedelic, with a serious delight in paradox. The DEI tracks disturbances in the field of probability by monitoring live data from casinos, which introduces a disquisition on the idea of money. Then, as Banacharski himself asks, if you can distort probability, what happens to necessity and free will? Probability itself is, as an MIT professor explains to Red Queen, only an idea – "an idea about expectation, or even desire". Since it's not an object or a force that could be altered by a machine, all the evidence that that is what's happening is very improbable indeed – a suggestion that, to the directorate, makes it only more cogent.

Delighting in the paraphernalia of genre, Leith reserves the right to refuse its consolations. He ties knots in our assumptions about stories. He interrupts his narration to comment on the behaviour of his characters. He contorts the grammar of his sentences so as not to admit whether Red Queen is a woman or a man. When used in feminist fiction of the 1970s, this cumbersome device, the excluded pronoun, conveyed a point about cognitive sexism. Leith seems to have lugged it in for its own sake, a padlock for Schrödinger's catbox: the chance to leave another particle of probability unresolved.

At the same time his playfulness leads always to a kind of melancholy. The last known conversation of Banacharski, a meditation on genocide and the redemptive chimera that shimmers in the theory of multiple universes, touches tragedy. Another DEI agent, Jones, is an "apsychotic", clinically devoid of imagination. Unable to think of anything that doesn't exist, Jones inhabits a twilight world of existential bleakness that comes close to horror. For the purposes of the author, silliness is not camouflage but its opposite: a tantalising surface that attracts attention and draws it very much deeper.